Why and what is this?


Is this a mixture of mold and dirt? It doesn’t wash off with water, but it cleans up with my standard HW mix the same way algae fades away. I have a lot of houses in my area with this problem resulting in business for me. This vent is part of the home ventilation system in the newer homes.


looks like moist air is venting out. Is it possibly a clothes dryer vent or range hood vent?


It is not a dryer vent or bathroom vent. These houses were built so tight that the builder had to incorporate a home ventilation system and it runs automatically. The homeowner can’t turn them off either. I believe its purpose is to help the house breath and prevent mold growth on the inside (just my opinion not fact).


I would bet money that’s a bathroom or dryer vent. Pushing out moisture causing growth like you said. I don’t think its an attic ventilation like @Rienmann thinks. Those are usually at the peak where the hottest part is. Just looks like repeat business in my opinion. tell them you can come back and clean it yearly!


If it cleans off with bleach, 99% of the time that means it’s organic in nature.

Whatever type of vent it is, it’s expelling air with high humidity, expediting the mildew growth.


A skinny horizontal window near the ceiling is indicative of a bathroom. It lets some light in without sacrificing privacy.


We run into these in every condo we do…builders build them “air tight” so they have a ventilation to push out/bring in new air. They are not always at the exact peak of the building.

There is a way for them to turn the vent motors off though. We cleaned 50 walls last year with those vents and then they had an HVAC guy come through and turn off all of the blowers for that vent.

It’s mold


@Patriotspwashing it is a ventilation system, that I do know as a fact. I assumed it was mold by the way it cleaned up. Thanks for everyone’s input! I guess it is caused by the constant moister from the ventilation.


Its called job security,you get them to turn it off there goes your newly found niche. Plus if its turned off then you have all that mold on the outside now growing on the inside with no way of cleaning it.


Had this sent to me this morn. Says its a dryer vent not sure yet tho havent been to scope it out yet tho. Gonna try just my hw mix on it, he has 20+ of these he wants done